Synthetic rubber compounds have been used to form a gasket inside a plastic closure for a container. The gasket has improved the seal between the closure and the container. The seal has been used to prevent leakage of the product out of the container and to prevent contamination of the product from outside air coming into the container.
The synthetic rubber compounds have been heated to a predetermined melting temperature before applying the molten synthetic rubber to the closure. In some prior systems the synthetic rubber has been mixed with an inert gas, such as nitrogen, to form a foamed gasket upon application to the closure. A Nordson Foam Melt model No. FM200 is an example of such a synthetic rubber and nitrogen gas applicator.
One suitable synthetic rubber compound that has been used is Foremelt 517/C, available from Foreco srl. (Marcallo Con Casone, Italy). Foremelt 517/C has a suggested application temperature of 175-180° Celsius.
The application has typically involved rotating the closure around a stationary applicator gun. The liquid synthetic rubber compound is applied from the gun to the closure. The closure is usually close to room temperature (20° C.) while the liquid synthetic rubber compound is applied. The synthetic rubber compound material may include a gas, such as nitrogen, to cause it to later become a foam. Because the closure is rotating during application of the liquid melted synthetic rubber compound, a ring shaped bead of foamed gasket forms all around the inside of the closure. Since the Foremelt 517/C is cold curing no further curing steps have been required, such as with a heated oven or microwave type oven. The closure with its gasket has then been applied to the container with the gasket providing the seal between closure and container.
However, product leakage has often been caused by inadequate bonding of the gasket to the closure. For food and beverage items, a gasket that separates from the closure after opening has not been acceptable. In some cases the gasket has fallen back into the container. In larger water cooler bottles gaskets with poor adhesion have shifted to one side allowing for leakage. In pressurized products, such as carbonated beverages, the pressurized gas has crept between the gasket and closure causing further gasket separation, escape of gas, and product spoilage. Thus, further improvement has been desired to more securely bond the gasket to the closure, and this solution is provided by the following.